The invention provides a preparation method of a lignocellulose ester/sodium alginate composite spherical Fenton-like catalyst, and is applied to the field of wastewater treatment. The method comprises: drying and crushing cellulose solid waste to obtain cellulose solid waste powder; uniformly mixing the cellulose solid waste powder with an esterifying agent, ferric salt and/or ferrite; adding into a mechanical activation solid-phase reactor; performing ball-milling and esterification reaction; separating an esterification product and a milling ball to obtain a lignocellulose ester mixture; adding the lignocellulose ester mixture into a sodium alginate solution under the conditions of stirring, so as to obtain blended liquid; dropwise adding the blended liquid into a calcium chloride solution, performing cross-linking solidification and filtration to obtain a solidified and iron-supported gel ball; drying the solidified and iron-supported gel ball to obtain a target product. The cellulose solid waste and the like are taken as raw materials, waste materials are recycled, waste is controlled by waste, resource and high-value utilization of the cellulose solid waste is realized, and the obtained product can generate a Fenton effect. Moreover, the product is of a porous structure, and is excellent in wastewater treatment effect, free from secondary pollution, and high in recycling rate.